Undefined behaviour in SADFWrite

[Algunenano]

Running using gcc -fsanitize=undefined -fsanitize-undefined-trap-on-error:

Using host libthread_db library "/usr/lib/libthread_db.so.1".
Core was generated by `/un/dev_public/postgis/loader/.libs/lt-pgsql2shp -f /tmp/pgis_reg/dumper postgi'.
Program terminated with signal SIGILL, Illegal instruction.
#0  0x00005613a20ab07d in SADFWrite (p=0x0, size=32, nmemb=0, file=0x5613a2d4dc40)
(gdb) bt
#0  0x00005613a20ab07d in SADFWrite (p=0x0, size=32, nmemb=0, file=0x5613a2d4dc40)
#1  0x00005613a20b6436 in DBFWriteHeader (psDBF=psDBF@entry=0x5613a2d510c0) at dbfopen.c:237
#2  0x00005613a20b821f in DBFWriteHeader (psDBF=0x5613a2d510c0) at dbfopen.c:211
#3  DBFClose (psDBF=0x5613a2d510c0) at dbfopen.c:587
#4  0x00005613a20c21cf in ShpDumperCloseTable (state=state@entry=0x5613a2d447e0) at pgsql2shp-core.c:2191
#5  0x00005613a20ab80a in main (argc=<optimized out>, argv=<optimized out>) at pgsql2shp-cli.c:229

PR: ​https://github.com/postgis/postgis/pull/310

[Raul Marin]

In 16862:

Fix undefined behaviour in SADFWrite

Also addresses several gcc warnings
References #4189

[Raul Marin]

In 16863:

Fix undefined behaviour in SADFWrite

Also addresses several GCC warnings.

Closes #4189
Closes ​https://github.com/postgis/postgis/pull/310

[Raul Marin]

In 16864:

Fix undefined behaviour in SADFWrite

References #4189

[Raul Marin]

In 16865:

Fix undefined behaviour in SADFWrite

References #4189

[Raul Marin]

In 16866:

Fix undefined behaviour in SADFWrite

References #4189